Piano playback issue

I’m generally pleased with the playback function in Dorico, but there are some minor issues that I don’t know how to correct.

I have the following in the bass clef at the end of a new piece for solo piano in 6/8 time. The ties out of the tremolo are necessary because I don’t want the interval struck as a chord coming out of the tremolo. The trouble is that when I play this back there are unwanted notes sounding under the fermata when it’s notated with those ties, a sort of residue of the tremolo. When I remove the ties I get the sound I want, but the notation is wrong. I’ve tried fiddling with played durations in Play Mode, but nothing works. What can I do to have both the notation and the playback as I want it?

There’s also a sudden reduction in volume under the fermata, unlike the gradual diminuendo you’d expect with notes sustained by the pedal, even at PPP.

I should specify that I’m using Dorico pro 6.0, haven’t yet upgraded.

Remove one of the ties. The trem has to end with one of the notes struck albeit softly.